[chef] Re: Re: Re: precedence is different, so why are values merged

[aaron peterson < >]

Specifically, if your goal is to replace a default attribute that is
an array or hash - set by cookbook attributes files or by another role
- you will commonly either use node.set in a recipe (most typical) or
use override_attributes in a role or environment, but be wary of the
arms race you've entered.  The now deprecated use !merge: may seem a
bit duct tapey but allow(ed) granular control.  There are other ways
of manually replacing attributes, but they are less explicitly part of
the attribute model.


However... and this is where everyone can take a big step back... if
this doesn't fit your needs, that's okay too.  The way attribute
resolution works is meant to be convenient and useful for most cases.
It turns out that there are lots of ways one could conceive of
merging, precedence, overlays, and other such constructs working.

So it's crucial to understand both how the model works and how to get
what you need.  Especially if it changes from time to time.  The
intent of the original design was, if I can read into it, to allow
"gathering" of data from a bunch of producers in the form of composed
roles and other sources.  For instance, imagine I have a nagios
cookbook that installs application- and service-specific checks based
on the contents of certain hashes.  With deep merging of attributes in
roles, As I build up an application stack with roles that provide
appropriate checks, the nagios recipe consumes the hash to produce all
of them in a single configuration, and I have a fully instrumented app
stack.  Now I can add additional specifications, alerts, thresholds,
etc. to, say, prod environments, and the existing cookbook implements
them as well.

-a

On Tue, Sep 18, 2012 at 11:59 AM, bradford 
<
 >
 wrote:
>
> I am still a little confused.  Perhaps someone could improve the docs
> a bit?  More clarification is needed on when merging takes place.  Is
> it always, unless you specify "!merge:"?  How do the
> default_attributes, normal_attributes, and override_attributes fit in
> with the precedence? The person I was talking to on IRC said he was
> bit by the same thing.  Or maybe it's just me and I am simply just
> reading through the docs too fast.
>
> On Tue, Sep 18, 2012 at 12:43 AM, Scott Kaminski
> <
 >
>  wrote:
> > I have encountered this exact problem before, when I was setting both
> > override and default attributes at the environment level.
> >
> > Array merging is covered here for roles/environments:
> > http://wiki.opscode.com/display/chef/Deep+Merge
> >
> > I ended up changing that setting to:
> > default['ntp']['servers']=Array.new
> >
> > Otherwise I ended up with an array list and setting of:
> > pool.ntp.org,pool2,ntp.org,myserver.whatever.com,mysecondserver.whaterver.com
> >
> >
> > Thanks,
> >
> >
> >
> >
> > On Mon, Sep 17, 2012 at 6:05 PM, bradford 
> > <
 >
> >  wrote:
> >> ntp has the following in attributes/default.rb:
> >>
> >>     default['ntp']['servers']  = %w{ 0.pool.ntp.org 1.pool.ntp.org
> >> 2.pool.ntp.org 3.pool.ntp.org }
> >>
> >> i added the following to my development.rb:
> >>
> >>     default_attributes( "ntp" => { "servers" =>
> >> ["0.north-america.pool.ntp.org", "1.north-america.pool.ntp.org"] })
> >>
> >> but i see all 6 of them in ntp.conf.  on irc someone said that when
> >> the precedence is the same, they get merged; but, according to the
> >> docs [1] the precedence is not the same:
> >>
> >> The precedence of the attributes - from low to high
> >>
> >>     default attributes applied in an attributes file
> >>     default attributes applied in an environment
> >>     default attributes applied in a role
> >>     default attributes applied on a node directly in a recipe
> >>     normal or set attributes applied in an attributes file
> >>     normal or set attributes applied on a node directly in a recipe
> >>     override attributes applied in an attributes file
> >>     override attributes applied in a role
> >>     override attributes applied in an environment
> >>     override attributes applied on a node directly in a recipe
> >>
> >> [1] 
> >> http://wiki.opscode.com/display/chef/Setting+Attributes+%28Examples%29